Filtration of solvent-water extracted tar sand



Aug. 5, 1969 Filed July 18,

A. M. BENSON 3,459,653

FILTRATION F SOLVENT-WATER EXTRACTED TAR SAND 1966 2 Sheets-Sheet 1 4 l 22 L g L2 -r FILTRATE 0 L I L J L -WM.L.. 1. .H 1. J. l

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INVENTOR ARNOLD M. BENSON BYZWIM.MIL "1/ HIS AGENT g 5, 1969 A. M. BENSON 3,459,653

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INVENTOR'.

ARNOLD M. BENSON 3,459,653 FILTRATION F SOLVENT -WATER EXTRACTED TAR SAND Arnold M. Benson, Oakland, Calif., assiguor to Shell Oil Company, New York, N.Y., a corporation of Delaware Filed July 18, 1966, Ser. No. 566,039 Int. Cl. Cltlg l /04 US. Cl. 20811 6 Clairns ABSTRACT OF TIE DISCLOSURE Recovering tar from tar sands employing a solvent extraction process wherein tar sand is slurried in a hydrocarbon solvent with sufficient water added to the slurry to form a grainy slurry, said water being from about 1% to about 7% by weight of the tar sand, and then filtering the slurry, whereby release of fines is controlled to maintain an easily filtered slurry.

This invention relates to a method of removing tar from tar sands. More particularly this invention relates to a method of removing tar from tar sands by solvent extraction with subsequent solvent recovery.

Large deposits of bituminous containing sand are found in various locations throughout the world and vary considerably in composition and properties. Some are relatively soft and free flowing while others are very hard or rocklike. The tar content of these sands may vary over a wide range and presents an attractive source of supply of crude petroleum. For example, one of the largest deposits of tar sands thus far discovered lies in the Athabasca district of Alberta, Canada, and extends for many thousands of square miles.

Various methods have been proposed in the past for the recovery of tar from these tar sands but none of the methods proposed has been entirely successful as far as the economy of the operation is concerned. Tar sands suffer the disadvantage of requiring additional processing steps over conventional forms of oil recovery. It is therefore essential that for any process to prove commercially feasible it must be competitive in price with other petroleum sources. It has been proposed to recover the tar content from tar sands by mixing the sands with water and separating the sand from the mixture formed. This process suffers the disadvantage of forming emulsions of water and oil which have been very diflicult to break, thereby resulting in considerable loss of product. Other methods utilize solvent extraction techniques but have been slow to filter, presumably due to an excess of fine particles in the sand. Still other methods have required the use of a multisolvent system whereby the tar sand is subjected to a series of solvents before it is finally recovered.

More efficient methods proposed recently in Ser. No. 537,902 filed Mar. 28, 1966, and in Ser. No. 537,903, filed Mar. 28, 1966, comprise extracting the tar from the sand by filtering the extraction solvent through a bed of tar sand thereby removing the tar from the sand and recovering the solvent from the tar depleted sand by means of steam stripping. The product recovered from the tar sands by these methods is dependent upon the extraction solvent utilized. In general, hydrocarbon solvents containing little or no aromatics will leave all or part of the asphaltene content on the sand while solvents containing a higher degree of aromaticity will extract all of the tar from the sand. Hydrocarbon solvents having from to 9 carbon atoms which have an aromatic content of from O to 50 percent by weight may be utilized.

One of the disadvantages of the above mentioned process is that not all tar sands filter uniformly. While the reasons for this are not exactly clear it is felt that the States Patent 0 3,459,653 Patented Aug. 5, 1969 tar content of the sand and the amount of the fines or small particles of sand greatly influence the rate at which solvent will pass through the sand.

Since tar sands having relatively high tar content filter more slowly than do those of lower tar content due to the viscosity of the extract, one method of solving this problem might be to use more solvent which would not be as economical, or to completely dissolve the tar off the sand prior to the filtration step. This latter step would require some sort of premixing operation such as slurrying. Even if this operation were successful it would not eliminate the problem of fines or other small particles which tend to plug the filter bed and impede filtration.

The problem of slurrying and fines in the filter bed are interrelated. It has been postulated that the fines and other small particles contained in tar sands are contained in water envelopes that surround individual grains of sand. These water envelopes are in turn surrounded by the tar or bitumen which is the desired product. In theory, if the tar sand is allowed to dry out or if the water envelope containing the fines is broken, these small particles are released and tend to plug the movement of liquid through the sand bed in any subsequent filtration operation.

Slurrying of the tar sands has not been considered to be practical due to the breaking of the water envelopes surrounding the grains of sand followed by the release of lines and other small particles into the slurry. Upon subsequent filtration of the slurry the bed would plug. Leary et al., US. Patent 3,117,922 propose to solve this problem by slurrying the tar sand under conditions sufficiently gentle that the water envelopes containing the fines are not broken but which are sufiicient to dissolve the tar or bitumen from around the water envelopes. This process required a two solvent system comprising a heavy solvent and a light solvent.

While the process of Leary et al. may prove practical for freshly mined tar sand in which all of the fines are encapsulated in a water envelope, it would not be applicable to a process in which the water had previously been dried out. This drying out may occur in a number of Ways. For example, during mining, transportation, and crushing operations prior to the slurrying step the tar sands tend to lose certain amounts of originally contained water. Moreover, this process requires a multisolvent system.

It has now been found that the tar can be etfectively and efficiently removed from the sand containing the same by a one solvent process which comprises slurrying the tar sands in a solvent in the presence of an added amount of water followed by filtration of the slurry and recovery of the solvent from the sand bed.

Presumably, the addition of water to the slurry causes the fines and other small particles to become encapsulated in water so as to prevent their disadvantageous migration and collection within the filter bed and to agglomerate them into masses that behave as larger particles.

This method allows tar sands which heretofore were thought to be impossible to process to be slurried and filtered at wholly acceptable rates.

FIGURE 1 shows a schematic flow diagram of one method of operating the process. FIGURES 2-5 show comparative runs made by slurrying a tar sand with solvent with and Without added water followed by filtration.

The amount of water to be added to the slurry may vary once a critical level has been established. Presumably this level is established at a point at which all or substantially all of the fines contained within the tar sand bed become encapsulated in water and may vary depending upon the amount of water already in the sand and upon the amount of fines contained in the sand. In general amounts of water between 1 and 7% by Weight, basis tar sand, are sufficient. The filtration rates of tar sand appear to be relatively insensitive to the amounts of fresh water added during slurrying once this critical level has been reached and the upper limit would be dictated by that point at which an emulsion between the tar and added water would form.

The extraction solvent consists of a volatile hydrocarbon fraction containing from about -9 carbon atoms per molecule and may be aromatic or non-aromatic depending upon the amounts of tar to be dissolved. Tar rich solvent obtained from filtering the slurry may also be used in place of or in addition to the C -C hydrocarbon as extraction solvent. In general, non-aromatic solvents such as heptane Will not dissolve the asphaltene content of the tar while aromatic solvents such as benzene and toluene completely dissolve the tar from the sands. It may be preferable to utilize a solvent such as heptane or other petroleum solvent fortified to a desired aromatic content by recycled tar rich solvent, benzene or toluene. The solvent preferably contains an aromatic content of from to 100% and more preferably between and 75%. It is also desirable that the extraction solvent be made up of both fresh solvent and recycled tar rich extract from the filtrate. The amount of solvent added to the tar sand to form a slurry is generally proportional to the amount of tar on the sands. Solvent to original tar ratios between 2:1 and 6:1 by volume may be used. The solvent, water, and tar sand may be mixed together in any manner desired to form the slurry.

It may be desirable to add only part of the total solvent to form the slurry and to add the remaining solvent to the filter bed once the slurry has been distributed on the filter. In this manner the latter solvent addition will serve to displace the tar rich extract from the bed and to wash out and dissolve additional amounts of tar on the sand not extracted in the slurry. The ratio of total solvent to original tar used in the process may vary from about 2: 1 to 10:1 by volume.

The invention may best be described by reference to FIGURE 1 which shows a schematic flow diagram of a method of operation.

The tar sand is first stripped of overburden and mined by appropriate means and brought to an extraction plant for removal of the oil and bituminous materials. This sand generally contains about 5 to percent by weight tar and 1 to 13 percent by weight water. The mined tar sand is then fed into appropriate machinery wherein it is crushed, broken or ground into proper size for solvent extraction.

The crushed tar sand is passed via line 1 into a slurry vessel 2 wherein it is contacted in any desired manner with solvent entering vessel 2 through line 3. The amount of solvent used will depend upon the tar content of the sand as earlier mentioned. An appropriate amount of water, generally between 1 and 3% by Weight basis tar sand, enters vessel 2 through line 4. The tar sand, solvent and water are mixed in vessel 2 in any appropriate manner such as propeller stirrers, paddles, fins, to form a slurry.

During the slurrying operation the tar is substantially all dissolved from the sand and the fine particles are encapsulated in water. It is this part of the process that greatly enhances the filtration rate of the slurry once it has been deposited on a filter. Certain patterns of behavior have been noted during this step of the operation. For example, slurrying poorly filtering sands without the addition of water produces a thin, smooth flowing slurry. This is consistent with observations in slurry flow where addition of fine particles make a slurry more free flowing and smooth. Apparently the fine particles act as a lubricant and give the slurry a thinner consistency than a slurry made up of larger particles. When filtered, this free flowing slurry deposits a layer of clay-like material at the top of the filter bed. Local pressure gradient measurements indicate that in a majority of cases the bulk of the pressure drop occurs in the upper layer of the bed; however, in some cases plugging at the bottom of the bed has occurred first. Agitation of the bed surface produces immediate improvement in filtration rate which ceases when agitation is stopped. This clay-like layer is absent at high filtration rates.

'In contrast, those sands which slurry with difiiculty, producing, thick, grainy suspensions which ooze rather than flow smoothly have high filtration rates. However, air drying of such a sand prior to slurrying produces a thinner slurry as which filters poorly as described below.

The addition of water to these smooth flowing thinner slurries produces a dramatic thickening of the slurry, eliminates the clay-like layer atop the settled filtration bed and significantly improves filtration rate.

The slurry formed in vessel 2 is then passed via line 6 to a filter 7. This filter may be a continuous belt filter, moving pan or rotary pan filter and the like or a series of such filters. The slurry is uniformly distributed on the filter thereby forming a bed of a predetermined thickness, e.g., between 3 to 12 inches. A pressure drop of from about 1 to 10 psi. is maintained across the filter bed by applying a vacuum or other appropriate means at the bottom of the filter bed or by means of applied pressure above the bed. The extract containing the solvent and dissolved tar is forced out of the bottom of the bed through line 8. If desired, additional solvent may be fed onto the filter bed '7 by means of line 9. The rate of filtration of the extract and solvent through the bed of sand in a. function of pressure drop across the bed, extract viscosity and particle size of the sand in the bed. Without the addition of water in the slurry to encapsulate and agglomerate the fines and other small particles the filtration rates tend to be somewhat slow for some tar sands. However, the addition of water to the slurry produces the above defined thick, grainy slurry which has a relatively high filtration rate. Generally, filtration rates between 2 g.p.m./sq. ft. and 10 g.p.m./sq. it. are to be expected. The extract entering line 8 from filter 7 is passed into a solvent recovery zone 12 wherein the solvent is separated from the tar and the tar is passed through line 13 for further processing and subsequent refining. If desired a portion of the extract may be recycled through line 10 back to line 3 to be used in the place of or in addition to the hydrocarbon solvent. In this manner a more efiicient use is made of the solvent. The recovered solvent is passed via line 14. into solvent storage tank 16 for reuse. The solvent rich, tar depleted sand remaining on filter 7 is passed through line 18 to solvent recovery zone 19. This zone preferably consists of the same type of filter apparatus used in filter 7 and can, in a batch operation, be the same apparatus. In solvent recovery zone 19 the solvent may be separated from the sand in any manner desired. Preferably it is stripped off by means of steam entering zone 19 through line 20. The steam is pushed or pulled through the sand bed by means of a pressure drop across the bed, thereby stripping ofi the solvent. The solvent and condensed steam leave the solvent recovery zone through line 21. The moist sand from zone 19 is pumped or conveyed through line 22 to a tailings area or otherwise disposed of. The recovered solvent from line 21 is fed into solvent storage tank 16 where it joins recovered solvent from solvent-tar separation zone 12. Any water contained in the solvent phase separates and is withdrawn via line 24. The recovered solvent in tank 16 may then be recycled through line 25 to join fresh solvent in line 9 for further slurrying and tar extraction.

The following examples are indicative of the way in which the addition of small amounts of water to a tar sand extraction solvent slurry greatly enhances the filtration rate of the slurry extract through a filter bed of tar sand formed by depositing the slurry on a filter. In each of the following examples the slurry vessel consisted of a 6-inch diameter section of glass pipe with a draft tube which was perforated with holes to allow stirring during the addition of sand to solvent. A marine Propeller was inserted in the draft tube. The vessel had a dished bottom which was split to drop away in two pieces. A thin rubber diaphragm provided a liquid seal during slurrying. In normal operation the raw tar sand was slurried with solvent for three to ten minutes at 700 to 1000 rpm. The diaphragm was then slashed and the bottom opened to discharge the slurry to a filter vessel directly below. Additional solvent was then drawn through the filter bed under vacuum. The filter vessel had an area of about 0.2 square feet and would have a hand bed of about 4 to 6 inches deep. A pressure drop of about inches Hg was maintained across the bed. The filtration rates given are the cumulative rate for 2000 mls. of filtrate in gallons per minute per square foot of area (g.p.rn./sq. ft.).

Example I FIGURE 2 graphically represents the results obtained from slurrying a tar sand sample containing 14.1% by weight tar wherein the tar sand, solvent and water proportions were as follows:

Filtration Wt. sand Toluene Water rate, g.p.m.

Run No (kg) (cc.) (00.) /sq. ft.

From the plot of filtrate collected versus time of FIG- URE 2 it is evident that the addition of water to the slurry increased the filtration rate at least 4.6 times.

Example II FIGURE 3 is also a graphical representation of the results obtained from a slurry of a tar sand containing 11.4% by weight tar. The proportions of sand, water and toluene were as follows:

Filtration wt. sand Toluene Water rate, g.p.m.-

Rnn No (k.g.) (00.) (00.) /Sq. ft

1 Bed plugged.

This example shows that the process of the present invention can make it possible to process and filter sands which would be impossible to process by a slurry-filter technique without the addition of water to the slurry.

Example III This example is graphically illustrated by FIGURE 4 and was carried out using a tar sand containing 10.1% by weight tar. The proportions used were the same as those used in Example II. Run No. 5 was made without added Water and filtered at the rate of 1.4 g.p.m./sq. ft. In contrast, when 100 cc. of water was added to a slurry of the same tar sand (run No. 6) the filtration rate increased to 3.8 g.p.m./sq. ft.

Example IV 6 Example V The following runs were made in the same manner as those in the preceding examples using a tar sand having a. uniform tar content of 12.8% by weight and show that the amounts of water added to increase the filterability of the tar sand is critical only up to a certain point and beyond that the filtration rates appear to be relatively insensitive to the amounts of fresh water added.

Filtration Wt. sand Toluene Water rate, g.p.m

Run N0 (kg) (00.) (00.) /sq. ft.

1 Plugged.

Analyses showed tar recoveries of about 95% at solvent/original tar ratios of 5.3 by weight. For this sand the critical water level of addition is about 2% by weight basis tar sand or 15% by weight, basis tar. The lower filtration rates for runs 17-19, employing 5 kg. of sand are probably a result of increased bed depth (6.5 inches vs. 5 inches) and the increased solution viscosity (36% w. tar vs. 26% W. tar in the slurry liquid).

I claim as my invention:

1. A process for the recovery of tar from tar sands which comprises the steps of (a) combining the tar sand with a hydrocarbon solvent and with added water to form a slurry of tar rich solvent and tar depleted sand, said hydrocarbon solvent being used in a ratio to original tar of 2:1 to 6:1 by volume, and said water being from about 1% to about 7% by weight of the tar sand slurried and in sufiicient quantity to form a grainy slurry, (b) depositing the slurry on a filter zone to form a filter bed and withdrawing therefrom the tar rich solvent as filtrate.

2. A process according to claim 1 wherein the hydrocarbon solvent contains from 5 to 9 carbon atoms.

3. A process according to claim 2 wherein the hydrocarbon solvent contains an aromatic content of at least 10%.

4. A process according to claim 3 wherein the hydrocarbon solvent also contains recycled filtrate from step (b).

5. A process according to claim 4 wherein additional hydrocarbon solvent is added to the filter bed in step (b) to assist in the removal of tar rich extract as filtrate.

6. A process according to claim 5 wherein a total of 2 to 10 volumes of solvent per volume of original tar on the sand is used.

References Cited UNITED STATES PATENTS 2,316,005 4/1943 Lachle 208-11 2,825,677 3/1958 Coulson 20811 3,392,105 7/1968 Poettmann et al. 208-11 OTHER REFERENCES The K. A. Clark Volume, Research Council of Alberta, Information Series No. 45, October 1963, I. H. Cottrell Paper, pp. 193-205.

DANIEL E. WYMAN, Primary Examiner P. E. KONOPKA, Assistant Examiner 

